Enhancement of lymph node metastasis and distant metastasis of thyroid carcinoma

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Abstract
BACKGROUND The mechanisms of local and distant metastases are imperfectly understood. The goal of the current study was to add to the body of knowledge regarding local and distant metastases of thyroid malignancies. METHODS The authors performed multivariate analysis of 573 patients who underwent surgery between November 1994 and May 2002 for follicular (FTC; n = 100), papillary (PTC; n = 236), or medullary thyroid carcinoma (MTC; n = 237) at a university hospital. RESULTS In multivariate analysis, extrathyroidal extension consistently evolved as the key risk factor for both lymph node metastasis and distant metastasis. This correlation was most pronounced in MTC and least pronounced in FTC. The risk of lymph node metastasis also increased with reoperative status in patients with MTC and with primary tumor diameter in patients with MTC (tumor diameter > 10 mm) and patients with PTC (tumor diameter > 20 mm). In the PTC group, lymph node metastasis was more common among patients younger than age 45. In the MTC group, extrathyroidal growth and distant metastasis were associated exclusively with lymph node metastasis. Lymph node metastasis was the only secondary risk factor for distant metastasis. In the analysis of risk factors for distant metastasis in the FTC and PTC groups, no interaction was found between extrathyroidal growth and lymph node metastasis. This finding suggests that extrathyroidal growth and lymph node metastasis of FTC and PTC, and presumably also MTC, represent separate mechanisms and routes of distant metastasis. CONCLUSIONS Screening for both local residual disease and distant metastases should be intensified in the high‐risk population of patients whose primary tumors exhibit large diameters, extrathyroidal growth, or lymph node metastasis. Cancer 2003;98:712–9. © 2003 American Cancer Society. DOI 10.1002/cncr.11581